Analysis of electrocardiogram data taken over extended periods provides clinically significant information which is important in the diagnosis and treatment of cardiac disease. Long-term recording of electrocardiographic data, commonly referred to as "Holter" monitoring, is a standard, accepted technique for electrocardiographic analysis. This amounts to recording electrocardiogram data over a period of time and subsequently analyzing that data for rhythmic and morphological changes.
Presently used monitoring devices for ambulatory patients are adequate for recording electrocardiogram data over twentyfour hour periods. However, presently used devices have limitations which come into play when longer term recording of electrocardiogram data is necessary.
Often it is desirable to monitor cardiac rhythm and disturbances in cardiac rhythm when the disturbances are highly variable in frequency or when the frequency of disturbances is very low. Current practice is to employ repetitive twenty-four hour cardiogram monitors. However, this is very expensive and results in significant discomfort to the patient due to the substantial size of the recording device required to record cardiac rhythm over twenty-four hour and longer periods.
For other patients, whose arrhythmia is symptomatic (meaning that the arrhythmia is related to a particular condition occurring in the patient's body which the patient can sense) a patient-activated cardiac event recorder is often used. These patient-activated cardiac event recorders are limited in the data they provide because the recorder must be activated by the patient. Obviously, if the arrhythmic event incapacitates the patient, the patient cannot activate the cardiac event recorder. Also, if the arrhythmic event is asymptomatic, a patientactivated cardiac event recorder cannot be used because the patient does not know when his or her arrhythmia is occurring.
Applicants are aware of printed prior art consisting of U.S. Pat. Nos. 4,123,785; 4,231,374; 4,333,475; 4,336,810 and 4,667,682.
The '785 patent discloses a cardiac event recorder for recording cardiac events over a defined twenty-four hour period. This device has the disadvantage associated with all patientactivated devices, namely if the arrhythmic event incapacitates the patient, the patient cannot activate the cardiac event recorder. Similarly, if the arrhythmic event is asymptomatic, a patient-activated device will never be turned on to record the arrhythmic event.
The '475 patent uses a microcomputer to continuously monitor analog electrocardiogram signals and execute algorithms to classify each heartbeat and tally abnormal events such as arrhythmia.
Similarly to '475, the 3 374 patent discloses a device and method for constantly monitoring heartbeat and activating circuitry upon occurrence of an abnormal heartbeat or other arrhythmic event to determine whether additional arrhythmic events occur during a selected subsequent monitoring period.
The '810 patent discloses method and apparatus for analyzing a Holter-type electrocardiogram utilizing a tape playback unit having an analog signal output representing electrocardiogram complexes.
The '682 patent discloses an ambulatory electrocardiogram recorder that senses tachycardia and bradycardia conditions and activates a tape recorder for a period of fifteen seconds after a traycardia or bradycardia event is detected.